1. Field of the Invention
The present invention pertains to cellular telecommunications, and particularly to allocation and release of radio channels for data services.
2. Related Art and Other Considerations
In recent years cellular telephones have become increasingly popular. A cellular telephone is just one example of what is referred to in telephone parlance as a xe2x80x9cmobile stationxe2x80x9d or xe2x80x9cmobile terminalxe2x80x9d. Telecommunications services are provided between a cellular telecommunications network and a mobile station (e.g., cellular telephone) over an air interface, e.g., over radio frequencies. At any moment an active mobile station is communicating over the air interface with one or more base stations. The base stations are, in turn, managed by base station controllers (BSCs). The base station controllers are connected via control nodes to a core telecommunications network. Examples of control nodes include a mobile switching center (MSC) node for connecting to connection-oriented, circuit switched networks such as PSTN and/or ISDN, and a general packet radio service (GPRS) node for connecting to packet-switched networks such as Internet, for example.
A mobile station can take on various forms other than a cellular telephone, including a computer (e.g., a laptop computer) with mobile termination capabilities. In some forms, mobile stations are capable of engaging in differing types of services, or multimedia services. In other words, the mobile station can execute several differing types of programs (i.e., xe2x80x9capplicationsxe2x80x9d) which interact with the user. Examples of these applications include Internet browsers and electronic mail programs. Several multimedia applications may reside in the same mobile station.
One type of standardized mobile telecommunications scheme, utilized, e.g., in Europe, is the Global System for Mobile communications (GSM). GSM includes standards which specify functions and interfaces for various types of services. A relatively recent data service available within the GSM system is General Packet Radio Service (GPRS). GPRS differs from existing data services in that GPRS is a packet switched service instead of a circuit switched data service. Whereas (in GSM) a circuit switched data user is connected continuously to the radio network during a data call (e.g., even when not transferring data), a GPRS user is connected to the radio network only when either (1) the mobile station desires to transmit or (2) the network has something to transmit to the mobile station. In other words, in GPRS the mobile station (e.g., a computer with mobile termination) is not connected to the network constantly while the computer is in use, but only during these two transmission events.
The GPRS service is provided to a connection over a GPRS packet data channel (PDCH). Before a GPRS packet data channel is reserved for a connection requesting such reservation, the GPRS packet data channel must first be allocated to GPRS from a pool of channels also available to other data services and to speech services. A list of the available channels in such pool, known as the GSM Idle List, is maintained at the base station controller.
Allocation of a packet data channel involves not only performance of a GPRS channel allocation procedure at the base station controller (BSC), but also performance of a GPRS channel activation procedure (e.g., at the base station). Whereas the time required at the base station controller to allocate a packet data channel is rather short (on the order of one to two milliseconds), the time required for the GPRS channel activation procedure is considerably longer (e.g., approximately one hundred milliseconds).
The standards documents concerning the GSM are relatively silent regarding GSM channel allocation. Regarding channel activation, the GSM standards documents describe that a channel is chosen first by the base station controller and then GSM channel activation is performed. In this regard, see the GSM Technical Specification 08.58 Version 5.2.0, July 1996.
GSM prescribes a channel release procedure whereby the base station controller releases a radio channel which is no longer needed. In accordance with this GSM channel release procedure, the channel being released is returned to the GSM Idle List maintained by the base station controller. The base station controller also sends an RF CHANnel RELease message to the relevant transmitter/receiver at the base station, specifying the channel-to-be-released. After having released the addressed sources, the base station sends a RF CHANnel RELease ACKnowledge message to the base station controller.
In view of the characteristics of GPRS as above described, fast access to GPRS is imperative. The existing circuit switched scheme for accessing and releasing channels is not ideal for GPRS. In the existing circuit switched scheme, a channel is released when it is deallocated. But if a channel has to be allocated again subsequently, it must again undergo the time-intensive channel activation procedure.
What is needed therefore, and an object of the present invention, is a fast channel allocation and an appropriate release procedure, such as for GPRS, for example.
A telecommunications system comprises a control node and a base station node. The control node maintains a first list (GSM Idle List) of idle radio channels which is consulted in order to obtain channels for a first type of telecommunications service. A second list (GPRS Idle List) of idle radio channels is maintained for a specialized telecommunications service, the idle radio channels of the second list being radio channels which are unallocated with respect to the specialized telecommunications service but yet activated (e.g., having an established transmission path and synchronization between the control node and a base station node). The second list of idle radio channels is initially consulted in order to obtain channels for the specialized telecommunications service. If no channels are available for the specialized telecommunications service on the second list, idle channels from the first list are adapted and utilized for the specialized telecommunications service. The specialized telecommunications service preferably involves packet data transfer (e.g., GPRS).
In one embodiment, the control node is a base station controller, and the second list is maintained at a packet control node. The packet control node can be co-located with the base station controller.
As one aspect of the invention, any potential capacity problem is addressed by providing timers for channels on the second list (GPRS Idle List). There is one timer corresponding to each channel on the second list, which timer is started when there is no more traffic ongoing on that channel. The channel remains activated with respect to the specialized telecommunications service, which makes fast specialized service access possible for all such users in that cell. As long as the timer has not expired, the channel on the second list is available for specialized service traffic without any new activation. However, when the timer expires, the channel is released and put on the first list, where it is once again available for all traffic. The timer values can be dynamically adjusted or varied, e.g., depending on processor load or traffic load at a cell.